The first step of RNA processing involves capping at the 5’ end. A methylated-guanosine connects to the phosphates at the 5’ end of the mRNA.
Next, a polyA tail is added to the 3’ end. The 3’ end of a eukaryotic mRNA is shortened, and the enzyme Poly(A) polymerase adds a tail of about 200 ‘A’ nucleotides to the 3’ end.
Lastly, introns are removed from the pre-mRNA through splicing.